Tachometer circuit for an internal combustion engine or the like

ABSTRACT

A tachometer wherein the current for the charging capacitor of the tachometer measuring circuit and the current for energizing the coil of the relay switch in the circuit, are from a single source, the tachometer having incorporated in its circuit an arrangement to permit its universal use on four-cycle engines with four, six, or eight cylinders, and having the further provision wherein the capacitor may be charged by the multiple pulsing from the center of low-tension magneto, assuring a sufficient amount of current per unit of time for full zener control. A further improvement in switching provides a similar universal feature on three ratios of two-cycle engines.

limited States Patent Westberg [451 Jan. 18, 1972 [72] lnventor: VivianLuther Westberg, 3400 Westach Way, Sonoma, Calif. 95476 221 Filed: Nov.12,1969

211 Appl.No.: s7s,94o

Parmater ..324/70 FOREIGN PATENTS OR APPLICATIONS 264,922 4/1964Australia ..324/169 Primary Examiner-Michael .l. Lynch Attorney-EdwardC. Threedy [57] ABSTRACT A tachometer wherein the current for thecharging capacitor of the tachometer measuring circuit and the currentfor energizing the coil of the relay switch in the circuit, are from asingle source, the tachometer having incorporated in its circuit anarrangement to permit its universal use on four-cycle engines with four,six, or eight cylinders, and-having the further provision wherein thecapacitor may be charged by the multiple pulsing from the center oflow-tension magneto, assuring a sufficientamount of current per unit oftime for full zener control. A further improvement in switching providesa similar universal feature on three ratios of two-cycle engines.

1 Claims, 8 Drawing Figures TACIIOWTER CIRCUIT FOR AN INTERNALCOMBUSTION ENGINE OR THE LIKE The novelty over the prior art of myimproved tachometer circuit resides in the fact that (l) the circuit maybe independently charged by a 6 v., 12 v., or magneto source; and (2) bythe use of a zener diode, the current required to charge the capacitorof the circuit and that used to operate the relay, is from the samepower source. In addition to the foregoing advantages and novelty overthe prior art, the employment of a selector switch and the use ofprecalibrated shunt resistors across the meter provides for selection offour, six, or eight cylinders on four-cycle engines, thus dispensingwith a multiplicity of components otherwise required for all four-cycleengines. Another switch arrangement provides selection of three ratioson two-cycle engines.

The invention consists of the combination and arrangement of parts shownin the accompanying drawings, in which:

FIG. 1 is a schematic diagram of my improvedfour-cycle tachometercircuit;

FIG. 2 is a schematic diagram of my improved two-cycle tachometercircuit showing a variation thereof;

FIG. 3 is a schematic diagram of a tachometer circuit similar to thatshown in FIG. 1, but. illustrating a further modification for low speedon low tension magnetos;

FIG. 4 is a schematic diagram of a tachometer circuit in which arotating magnet is used to actuate the relay switch embodied in thecircuit;

FIG. 5 is a schematic diagram of a tachometer circuit showing a furthermodification over that shown in FIG. 2;

FIG. 6 is a schematic diagram of a tachometer circuit similar to thatshown in FIG. 1, but showing the employment in the circuit of a fullwave rectifier bridge;

FIG. 7 is a schematic diagram of a tachometer circuit similar to thatshown in FIG. 6, but illustrating a further modification; and

FIG. 8 is a schematic diagram of a tachometer circuit similar to 'FIG.6, but showing incorporated therein a transistor driving network.

Referring particularly to FIG. 1 showing one form of the invention,there is'employed in the tachometer circuit a conventional-type meter 10for indicating the r.p.m.s of an internal combustion engine. There isalso employed in such tachometer circuit a relay 1] of the conventional,type comprising an armature 12 having oppositely disposed contacts 13and 14 engageable with stationary contacts 15 and 16, respectively.

The armature 12 is actuated by a coil 17. The armature 12 by a conductor18 is connected to one side of a charging capacitor 19. By a conductor20, the opposite side of the capacitor 19 is connected as at 21 to aconductor 22. The conductor 22 connects one side 23 of the meter 10 tothepositive side of a 6 v. distributor of an ignition system of aninternal combustion engine when the terminal 24 is connected thereto. Ifa 12 v. distributor is to be utilized, then terminal 24' is connectedthereto in place of terminal 24. In the conductor 22 is a diode 25 whichallows passage of current from the power source in the direction of thecapacitor 19 but opposes its flow in an opposite direction. A commonlead conductor 26 for each of the terminals 24 and 24' when one or theother is used connects the stationary contact 16 to the conductor 22 ata point indicated at 27 below the diode 25. In this conductor 26 is apower resistor 27.

A conductor 28 connects one side of the coil 17 to the conductor 26 at apoint indicated at 29 in advance of the resistor 27. The opposite sideof the coil 17 is connected by a conductor 30 to the negative side orground 30' of the distributor of the engine. Extending between theconductor 22 and the conductor 26 and having incorporated therein azener diode 31 is a conductor 32. A filter capacitor 33 is connectedacross the I zener diode 3I.

As a constant-level voltage is essential for accurate meter reading, thezener diode 31 is here used as a voltage regulator Connected as at 34 tothe conductor 26 below the resistor 27, is a resistor 35 connected by aconductor 36 to the positive side 24' of a 12 v. distributor or otherpulsing device.

The purpose or function of the resistor 35 is to drop the voltage to alevel compatible with the relay coil 17 and the meter 10, thus toprotect the circuit from overload. The resistor 27 forms the powersupply for the zener-charging system.

The frequency with which the capacitor 19 is charged and discharged isproportionate to the r.p.m.'s of the engine. By providing the meter I0responsive to the current transferred by the capacitor 19, the frequencyof operation of the relay I l and therefore the r.p.m.s of the engine,may be directly indicated on the meter l0. This result is brought aboutin the following manner:

Normally the contact 13 is in contact with the stationary contact 15,connected by a conductor 44 to one side of the meter 10, with the resultthat an electric charge or impulse is discharged into the meter 10. Uponenergizationcf the coil 17, the armature 12 is biased against the actionof a spring 37, bringingthe contact 14 thereof into contact with thecontact 16, thus to charge the capacitor 19 at each pulse. Since thevoltage of the current to the capacitor 19 is regulated by the zenerdiode 31, the capacitor 19 is charged to a constant voltage value eachtime the relay is energized to make and break contact between thecontacts 14 and 16 and 13 and 15, respectively, the capacitor 33 beingused to insure full zener voltage throughout pulse cycle.

As herein described and as shown in FIG. I, the tachometer circuit abovedescribed may be used with either a 6 v. or a 12 v. source without inany way changing the relationship between the componentparts of thetachometer circuit.

A filter capacitor is by line 39 connected across the contacts of themeter 10 to insure complete discharge of the capacitor 19 in minimumtime. A resistor 39' of 100 ohms is placed in line 39 to prevent anypossible pitting between the contacts of slow-speed tachometers.

Incorporated in the circuit shown in FIG. 1, is a selective switch 40including a blade 40 adapted to selectively engage contacts 41, 42 and43 connected to the conductor 44 through precalibrated shunt resistors41', 42' and 43 each of a different predetermined value requisite to thetype engine with which the tachometer is used, to automaticallycalibrate the meter for corrected reading for either four, six, oreightcylinder engines.

By such an arrangement, only one tachometer is required for accuratereading of r.p.m.sof four, six, or eight-cylinder engines.

I A tachometer having the features herein described performs with a highdegree of accuracy due to zero resistance of silver contacts of relay.This is not true with transistor or similar energy transfer units. Thiszero resistance also eliminates errors of other systems with change oftemperature from l50 F. to +1 50 F.

The tachometer circuits illustrated in FIGS. 2 to 8 inclusive aresimilar to that shown in FIG. 1, with certain modifications for themeter circuit. The capacitor 33 is used to store sufficient power frompulse to insure full full zener-regulated voltage throughout the pulsecycle for charging the capacitor 19.

which will be presently made apparent. The components included in eachof the circuits of FIGS. 2 to 8 inclusive which are common to those usedin the circuit of FIG. I, will be referred to by the same referencenumerals.

In this connection, referring specifically to FIG. 2, the armature 12 ofthe relay 11 is connected to one side of a capacitor 45, the oppositeside of such capacitor being connected to two contacts 46 and 47 of athree-point switch 48. The third point 49 of the switch 48 is connectedto a contact 50 of a switch 51, the switch 51 being connected as at 52to the armature 12. A second capacitor 53 is connected between thecontact 50 and the contacts 46 and 47 of switch 48, which switch 48 isconnected to the conductor 22. Connected across the capacitor 38 is avariable resistor 38' to calibrate the meter 10 when switch 48 is in theposition shown in FIG. 2, with the contact 46 engaged.

The arrangement is such that by adjustment of the switches 48 and 51,the equally matched capacitors 45 and 53 are connected in parallel,connected singly, and then both connected in series when the contact 49is engaged. Thus only one calibration by resistor 38 provides accuratecalibration of all three ratios, one-half, land 2 on two-cycle enginesand engines inherent with such capacitor connections. This simplifiedcalibration and ease of selecting equal matched capacitors insuresmanufacturing economy.

The tachometer circuit illustrated in FIG. 3 is especially designed-foruse in connection with low speed engines, for example, 500 r.p.m.s.,where the relay pulse is taken from each cylinder and the zener powerfrom all cylinders. This multiple pulse provides sufficient powercoverage across the zener diode 31 and the capacitor 33 for zenervoltage control.

One side of the coil 17 is by a conductor 54 connected to the conductor22 and to the ground side indicated at 30'. The opposite side. of thecoil 17 by a conductor 26' is connected through a cylinder terminal 23'to the positive side of the single coil of a low-tension magneto. In theconductor 54 is incorporated a resistor 55 whichpowers the zener diode31 from the undistributed center of the low-tension magneto, theresistor 55 being the same as the dropping resistor 27.

To prevent ignition cutout there is incorporated in the conductor 22 achoke coil 56 that is connected to one side 23" to the center contact ofa magneto. The multiple pulse system shown in FIG. 3 is connected to thecenter of the distributor such thata sufficient number of pulses fromthe distributor assures an adequate supply of current per unit of time(for example, the distributor is operating to supply eight pulses persecond), to supply enough currentto the zener diode to main- I taintheproper voltage for the meter circuit.

The tachometer circuit shown in FIG. 4 basically is the same as thatshown in FIG. 1 except that in lieu of the use of a coil for'actuatingthe armature of the relay 11, there is employed a permanent magnet 57fixed to and rotatable with a shaft 58 connected to the device orengine, the speed of which is to be indicated by the meter 10. Thispermanent magnet 57 cooperates with a'pair'of posts 59 for vibrating thearmature 12 to alternately engage the contacts 13 and 14 thereof withthe contacts 15 and 16. The component parts of FIG. 1 which are used inthe circuit shown in FIG. 4 are designated by the same referencenumerals. To this circuit of FIG.' 4 can be added the switches 48, 51 toprovide a universal diesel tachometer.

The tachometer circuit shown in FIG. is a variation of the circuit shownin FIG. 2 and principally differs therefrom in that in lieu of the relayswitch of FIG. 4, the armature is actuated by the rotating permanentmagnet employed in FIG. 4.

The tachometer circuit shown in FIG. 1 has been modified in the mannerillustrated in FIG. 6. In the circuit shown in FIG. 6', there isincorporated in addition to most of the components 60' to one side ofthe coil 17 and a full-wave rectifier network 61 connected by conductors61 and 62' to the secondary side of the transformer 60 and by conductors29 and 22 to the circuit of the tachometer. The opposite side of thecoil 17 by conductor 17' is connected to the negative side of a l v. AC

' power source 18. Thus, the relay operation is in phase with thepulsing of the power source 18 in the manner of a frequency meter. Suchan arrangement develops a constant regulated voltage across the zenerdiode 31. The resistor 62 is used to drop the l 15 v. AC current to avalue compatible with the regulated voltage of the meter circuit.

The tachometer circuit shown in FIG. 7 differs from that shown in FIG.6, in that in lieu of the relay switch there is employed the rotatingpermanent magnet of the circuit shown in FIG. 4, for actuating theannature.

The tachometer circuit shown in FIG. 8 is a variation over that shown inFIG. 6, in that in lieu of the full-wave rectifier 'shown in FIG. 1, atransformer connected by a conductor network and transformer as employedin the circuit shown in FIG. 6, there is employed in FIG. 8 a transistor63. The base of the transistor 63 is connected by a conductor 64' to aterminal 64 of an ignition coil (not shown). The conductor 64' hasincorporated therein a power resistor 65. The emitter of the transistor63 is by a conductor 66 connected to one side of the relay coil 17. Theconductor 66 has incorporated therein a diode 63 permitting flow ofcurrent only to the relay coil 17.

The collector of the transistor 63 by a conductor 22' is connected tothe conductor 22 in turn connected to one side 23 of the meter 10. Inthe conductor 22 is incorporated a resistor 67, the conductor 22 beingconnected to a 12 v. positive terminal 67 The coil 17 is grounded by theconductor 31'. In

this circuit the current is amplified in magnitude by the transistor 63to a value which is sufiicient to operate the relay coil 17 forobtaining accurate meter reading.

The amplification of the current is desirable where the effective poweron the primary of an ignition coil is of insufficient duration toactuate the relay, with the result that without such amplification aninaccurate reading on the meter would result.

The conductors incorporated in the various circuits shown in FIGS. 1 to8 inclusive are relatively short and when the components are assembledas a unit, a compact unit results.

While I have illustrated and described the preferred form ofconstruction for carrying my invention into effect, this is capable ofvariation and modification without departing from the spirit of theinvention. I, therefore, do not wish to be limited to the precisedetails of construction set forth, but desire to avail myself of suchvariations and modifications as come within the scope of the appendedclaims.

Having thus described my invention, what I claim as new and desire toprotect by Letters Patent is:

1. An improvement in a tachometer circuit including a meter, a relayswitch operated by a relay coil to alternately engage contacts toactuate the meter, wherein the improvement comprises a. a pair ofterminal connectors for selectively connecting one side of the meter toa positive terminal of an electrical pulsing power source of determinedvoltage,

b. a conductor connected to one of said pair of terminal connectors andconnected to one side of the meter 10 and including a diode that permitsflow of current through the conductor in the direction of the meter,

c. a line connection including a series of bleeding resistors connectedin parallel with the other side of the meter and one stationary contactof the relay switch and having a switch for selectively connecting oneof the resistors to the meter,

d. a second line connection between the other stationary contact of therelay switch and said first-mentioned conductor at a point between themeter and the diode and including a voltage dropping resistor,

e. a second conductor connecting one side of the relay coil to saidfirst-mentioned conductor between the diode and the meter and includinga zener diode,

f. a ground connection for the opposite side of the relay coil,

g. a movable contact of the relay switch connected to saidfirst-mentioned conductor and including a capacitor having one sideconnected to said first-mentioned conductor and an opposite side to themovable contact, h. a filter capacitor connected between said secondline connection and said first-mentioned conductor in parallel to saidcapacitor and said zener diode,

i. and a line connection for said other of said pair of terminalconnectors including a dropping resistor connected to saidfirst-mentioned conductor between said one of said terminal connectorsand said diode.

1. An improvement in a tachometer circuit including a meter, a relayswitch operated by a relay coil to alternately engage contacts toactuate the meter, wherein the improvement comprises a. a pair ofterminal connectors for selectively connecting one side of the meter toa positive terminal of an electrical pulsing power source of determinedvoltage, b. a conductor connected to one of said pair of terminalconnectors and connected to one side of the meter 10 and including adiode that permits flow of current through the conductor in thedirection of the meter, c. a line connection including a series ofbleeding resistors connected in parallel with the other side of themeter and one stationary contact of the relay switch and having a switchfor selectively connecting one of the resistors to the meter, d. asecond line connection between the other stationary contact of the relayswitch and said first-mentioned conductor at a point between the meterand the diode and including a voltage dropping resistor, e. a secondconductor connecting one side of the relay coil to said first-mentionedconductor between the diode and the meter and including a zener diode,f. a ground connection for the opposite side of the relay coil, g. amovable contact of the relay switch connected to said first-mentionedconductor and including a capacitor having one side connected to saidfirst-mentioned conductor and an opposite side to the movable contact,h. a filter capacitor connected between said second line connection andsaid firstmentioned conductor in parallel to said capacitor and saidzener diode, i. and a line connection for said other of said pair ofterminal connectors including a dropping resistor connected to saidfirst-mentioned conductor between said one of said terminal connectorsand said diode.